pHValueProperty.link( function( pH ) {
if ( pH !== null && pH !== solution.pHProperty.get() ) {
solution.soluteProperty.set( Solute.createCustom( pH ) );
}
upArrowNode.setEnabled( pH < PHScaleConstants.PH_RANGE.max );
downArrowNode.setEnabled( pH > PHScaleConstants.PH_RANGE.min );
} );
drag: function( event ) {
// If the solution volume is zero (empty beaker), then we have no solution, and therefore no pH, so do nothing.
if ( solution.volumeProperty.get() !== 0 ) {
// Adjust the y-coordinate for the offset between the pointer and the indicator's origin
var y = event.currentTarget.globalToParentPoint( event.pointer.point ).y - clickYOffset;
// Convert the y-coordinate to a model value
var value = yToValue( y );
// Map the model value to pH, depending on which units we're using.
var pH = ( graphUnitsProperty.get() === GraphUnits.MOLES_PER_LITER ) ? concentrationToPH( value ) : molesToPH( value, solution.volumeProperty.get() );
// Constrain the pH to the valid range
pH = Util.clamp( pH, PHScaleConstants.PH_RANGE.min, PHScaleConstants.PH_RANGE.max );
// Instantiate a new 'custom' solute with the desired pH, and use it with the solution.
solution.soluteProperty.set( Solute.createCustom( pH ) );
}
}